Critical Vulnerability in Fluent Bit Logging Utility Threatens Major Cloud and Tech Companies

Critical vulnerability in Fluent Bit logging utility poses risks to major cloud and tech companies. Learn about Linguistic Lumberjack (CVE-2024-4323) and its mitigations.
TL;DR - A critical vulnerability named Linguistic Lumberjack (CVE-2024-4323) has been found in Fluent Bit, a widely used logging utility. This flaw can lead to denial-of-service attacks, information disclosure, and possibly remote code execution. The issue affects versions 2.0.7 through 3.0.3 and has been fixed in version 3.0.4. Users should upgrade immediately or mitigate by restricting access to the vulnerable API endpoint. Major cloud and tech companies using Fluent Bit should take prompt action to secure their systems.

Logging utilities are integral to modern cloud and tech infrastructures. They collect and process vast amounts of data, ensuring seamless operations and security monitoring. Fluent Bit stands out as a key player, widely adopted by industry giants like Microsoft, Google Cloud, and AWS. Recently, however, a critical vulnerability known as Linguistic Lumberjack (CVE-2024-4323) has been discovered, raising significant security concerns.

What is Fluent Bit?

Fluent Bit is an open-source data collector and processor designed for efficiency and scalability. Capable of handling large volumes of log data from diverse sources, it is a preferred choice for cloud-based environments. With billions of downloads and over 10 million daily deployments, its reliability and performance have made it indispensable for major tech companies.

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The Vulnerability: Linguistic Lumberjack (CVE-2024-4323)

Linguistic Lumberjack is a critical memory corruption vulnerability found in Fluent Bit’s built-in HTTP server. This flaw, introduced in version 2.0.7 and existing through 3.0.3, can potentially lead to denial-of-service (DoS) attacks, information disclosure, and possibly remote code execution (RCE). Such vulnerabilities pose severe risks, especially given Fluent Bit's widespread use across cloud infrastructures.

Technical Details

Fluent Bit’s monitoring API allows administrators to query internal service information. However it was discovered that the data types of input names were not properly validated. This oversight leads to memory corruption when non-string values are passed in the “inputs” array of a request.

For instance:

  • Large integer values can cause crashes due to memory overflows.
  • Negative values can overwrite memory, leading to service instability.
  • Specific values can expose adjacent memory, leaking potentially sensitive information.

These issues are particularly concerning as they can be exploited to cause service disruptions and data breaches. While remote code execution is possible, it requires precise conditions, making DoS and information leaks the more immediate threats.

Mitigations and Fixes

The developers have addressed this vulnerability in the main source branch, with fixes expected in version 3.0.4. Users are strongly advised to upgrade to this version to mitigate risks. For those unable to upgrade immediately, it is crucial to:

  • Limit access to the vulnerable endpoint.
  • Disable the impacted API endpoint if not in use.

Ensuring that only authorized users can query the API is a critical step in protecting against potential exploits.


Logging utilities like Fluent Bit are foundational to both cloud-based and on-premises infrastructures. As such, vulnerabilities within these tools can have far-reaching impacts. Organizations must prioritize regular updates and implement robust security measures, including the principle of least privilege and comprehensive monitoring, to safeguard their logging infrastructure against exploitation.


What is Fluent Bit?
Fluent Bit is an open-source data collector and processor that handles large volumes of log data. It is widely used for its scalability and efficiency.
What is the Linguistic Lumberjack vulnerability?
Linguistic Lumberjack (CVE-2024-4323) is a critical memory corruption vulnerability in Fluent Bit’s built-in HTTP server, potentially leading to DoS, information disclosure, and RCE.
How can Linguistic Lumberjack be exploited?
Exploitation can occur through malformed requests to Fluent Bit’s monitoring API, causing memory corruption and enabling DoS or data leakage. RCE is possible under specific conditions.
What are the potential impacts of this vulnerability?
The primary risks are denial-of-service attacks and information leaks. There is also a potential for remote code execution, though it requires precise conditions to exploit.
How can users mitigate this issue?
Users should upgrade to Fluent Bit version 3.0.4. If immediate upgrade is not possible, limiting access to the monitoring API and disabling unused endpoints are recommended steps.

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